We study arithmetic progressions {a, a+b, a+2b, . . . , a+(ℓ−1)b}, with ℓ ≥ 3, in random subsets of the initial segment of natural numbers [n] := {1, 2, . . . , n}. Given p ∈ [0, 1] we denote by [n]p the random subset of [n] which includes every number with probability p, independently of one another. The focus lies on sparse random subsets, i.e. when p = p(n) = o(1) as n → +∞.Let X ℓ denote the number of distinct arithmetic progressions of length ℓ which are contained in [n]p. We determine the limiting distribution for X ℓ not only for fixed ℓ ≥ 3 but also when ℓ = ℓ(n) → +∞. The main result concerns the joint distribution of the pair (X ℓ , X ℓ ′ ), ℓ > ℓ ′ , for which we prove a bivariate central limit theorem for a wide range of p. Interestingly, the question of whether the limiting distribution is trivial, degenerate, or nontrivial is characterised by the asymptotic behaviour (as n → +∞) of the threshold function ψ ℓ = ψ ℓ (n) := np ℓ−1 ℓ. The proofs are based on the method of moments and combinatorial arguments, such as an algorithmic enumeration of collections of arithmetic progressions.